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I’ve been chatting to the guys over at HBA, who’ve introduced me to the Nanadovic configuration (two fixed wings, zero horisontal gap between the TE of the front and LE of the rear wing) and the rear wing positioned about 1/3 chord below the front wing.
This is extremely close to the configuration I have been considering for the Tiby Cedar Flea. The only real difference is that the TCF wings can pivot. Below is a more modern Nanadovic example, with the two wings joined by a plane – which significantly increases wing rigidity.
Fascinating. According to “Cluttonfred”, a well-respected HBA contributor, who translated Nanadovic’s paper, Nanadovic did his graduate work in France in the 1930s notably in finding the most efficient combination of gap and stagger for a biplane wing. His conclusions were as follows:
“Recent experiments by M. Nanadovic at the St. Cyr laboratory show that with a particular configuration of a biplane, one can see improvements over a monoplane of the same profile of 25% less drag, 15% more lift, and 51% better speed range.”
This is remarkable, if true. And we have reason to doubt his academic findings. Nanadovic ascribes these results to the effect of the geometry of the two wings, which act to pull the airflow of the front wing over the rear wing (something the Flea community refer to as the “slot effect”.
So my idea to produce a low-wing Flying Flea seems to have support from Nanadovic. And that’s very encouraging.
One Comment
June 17, 2024 at 5:34 pm
Duncan, while both Nenadović and Mignet included the “slot effect” in one way or another to explain their configurations, the two are very different animals. The Mignet “living wing” uses variable incidence on the front wing, also creating a variable gap as the front wing tailing edge changes distance from the rear wing leading edge, with the aircraft CG between the aerodynamic centers of the two wings. The Nenadović biplane acts as essentially a slotted monoplane wing with defined, fixed gap/incidence and the aircraft CG forward of the net aerodynamic center of the “combined” wing. In other words, the Mignet configuration is a complete tandem wing system in itself but the Nenadović system is effectively a monoplane requiring a separate horizontal stabilizer of some kind. I think it’s dangerous to mix the two theories.